The goal in this study is to develop a cell-based assay to screen compounds for antiviral activity against certain members of the Togavirus family. We are particularly targeting the more pathogenic encephalitis-causing viruses from the alphavirus genus, such as Venezuelan equine encephalitis virus (VEEV), Eastern equine encephalitis virus (EEEV) and Western equine encephalitis virus (WEEV) which have been listed as category B bioterrorism agents. Sindbis virus and VEEV are prototypic alphaviruses that have been extensively used as vectors for expression of foreign genes. These agents provide us with useful systems to promote the development of an antiviral screening program based on alphavirus replicons. This screening program will focus on using Sindbis and VEE replicon systems for high-throughput screening of small molecules. Using an Old World virus (Sindbis) and a New World virus (VEEV) in screening provides us with an opportunity to find broad-spectrum anti-alphavirus compounds in order to better deal with species, quasispecies and unknown alphavirus pathogens. We propose the following specific aims: 1) generate cells that transiently or constitutively express a reporter gene from a VEE replicon; 2) validate the replicon cells for screening; 3) screen synthetic and natural compound libraries using both our existing Sindbis replicons and newly made VEE replicons; 4) confirm the anti-viral activity of the most potent compounds. These efforts will contribute to the goal of finding therapeutic modalities to control these important pathogens.